Physics and Applications of High Brightness Beams, Havana, Cuba March 28-April 1, 2016 Beam manipulation for resonant PWFA Enrica Chiadroni on behalf of the SPARC_LAB collaboration
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Physics and Applications of High Brightness Beams, Havana, Cuba !March 28-April 1, 2016
Beam manipulation for resonant PWFA
Enrica Chiadroni on behalf of the SPARC_LAB collaboration
Motivation❖ Plasma-based acceleration has already proved the ability to reach ultra-high, ~GV/m,
accelerating gradients!❖ J. Rosenzweig et al., Phys. Rev. Lett. 61, 98 (1988): First experimental demonstration of PWFA!❖ Mangles, Geddes, Faure et al., Nature 431, (2004): The dream beam !❖ W. P. Leemans, Nature Physics vol. 2, p.696-699 (2006): GeV electron beams from a centimetre-scale accelerator !❖ I. Blumenfeld et al., Nature 445, p. 741 (2007): Doubling energy in a plasma wake !❖ P. Muggli et al, in Proc. of PAC 2011, TUOBN3: Driving wakefields with multiple bunches !
❖ The next step is the extraction and transport of the beam, preserving its quality, i.e. 6D high brightness, stability and reliability to drive a plasma-based user facility (the EUPRAXIA Design Study has been funded from EU)!
❖ Litos, Nature 515, 92 (2014): High efficiency acceleration in the driver-trailing bunches!❖ S. Steinke et al., Nature 000 (2016) doi:10.1038/nature16525: Multi-stage coupling!
❖ Resonant excitation of plasma wakes increases !❖ energy transfer from driver bunches to the witness beam, encouraging the preservation
of the plasma-accelerated beam quality !❖ High brightness multi-bunch trains are mandatory for a significant improvement of the
efficiency of PWFA
Plasma-based Accelerators
❖ An intense, high-energy charged particle beam (driver) drives a high-gradient wakefield as it passes through the plasma !!
❖ The space-charge of the electron bunch blows out plasma electrons!!
❖ Plasma electrons rush back in and overshoot setting up a plasma density oscillation!!!
❖ A second beam (witness), injected at the accelerating phase, is then accelerated by the wake
ALaDyn sim., courtesy of A. Marocchino
! = !p =
s4⇡n0e2
me
Limitation of PWFA❖ PWFA acting as an energy transformer has the great potential to double beam energy in
a single stage!
❖ The energy transfer from the drive bunch to the plasma is optimized by maximizing the transformer ratio
R =|E+,max
||E�,max
| 2
Wakefield theorem*!❖ Symmetric drive bunch current profile in a single-mode
structure: the maximum accelerating field behind the drive bunch cannot exceed 2 times the maximum decelerating field amplitude along the drive bunch
F. Massimo et al., NIM A 740, 242–245 (2014) *V. V. Tsakanov, Nucl. Instrum. Methods Phys. Res., Sect. A 432, 202 (1999)
Enhancing Transformer Ratio
❖ Tailoring longitudinal current profile such that all longitudinal slices lose energy at the same rate!
❖ Asymmetric drive bunch current profile, !i.e. triangular, double triangle, doorstep-like !distributions, or multiple ramped bunch trains, !overcome this limit (R.Ruth et al., PA 1985; W. Lu et al.,!PAC 2009)
The maximum possible transformer ratio for a bunch with given length and total charge corresponds to that charge distribution which causes all particles in the bunch to see the same
retarding field*
*K. Bane, P. Chen, and P. B. Wilson, SLAC-PUB-3662,1985
❖ By properly tailoring the driver bunch shape, the witness beam energy might be more than doubled when
Courtesy of F. Massimo
Resonant PWFA
❖ Bunch spacing depends on the plasma density
�z = �p
�z0 ⇡ �p
2
�p(µm) ⇡ 3.3 · 104 n�1/2e (cm�3) = 330 µm @ ne = 1016 cm-3
❖ Multi-bunch shaping is one of the most promising candidates !❖ Increase in energy of a trailing particle !❖ Preservation of witness emittance and length!❖ Better control of the energy spread
Driver
Witness
�� = R�
Tailoring Beam ShapeFACET
❖ Notching device in a dispersing section !❖ High-efficiency acceleration of an electron beam in a plasma !
wakefield accelerator, M. Litos et al., Nature 515, 6 (2014)!
❖ Emittance Exchange (EEX) beam line and transverse mask!❖ Double triangular current profile (G. Ha et al., AIP Conf. Proc. 1507, 693 (2012))!
❖ Anisochronous dogleg beam line !❖ ramped bunch trains (R. J. England et al., PRL 100, 214802 (2008))!
❖ Multi-bunch via collimation: dogleg and multi-wire mask!❖ P. Muggli et al, PRL 101, 054801 (2008)!
❖ Beam shaping via photo-emission!❖ Laser comb generation and velocity bunching regime!
❖ Ramped bunch trains (NIM A 637, S43–S46 (2011)) !❖ The SPARC_LAB Experience
The SPARC_LAB Test Facility
https://www.google.it/maps/@41.8231995,12.6743967,3a,69.7y,130.68h,76.68t/data=!3m6!1e1!3m4!1sYyB35yaBMxJgQ92-wp3oYQ!2e0!7i13312!8i6656?hl=en
Thomson back-scattering beamline
External injection beamline
Undulator beamline
Test bench beamline
r-PWFA experiments
2 S-band structures 1 C-band structure
THz source
FLAME laser transport line (Ti:Sa laser, 300 TW, < 30 fs)
http://www.lnf.infn.it/~chiadron/index.php
Ti:Sa Laser
S-band RF gun
Sources for Plasma Accelerators and Radiation Compton with Lasers And Beams
Beam energy 90 – 180 MeV Bunch charge 50 – 700 pC Rep. rate 10 Hz εn!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!<!2 mm-mrad σγ!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!0.05%!'!1%!!Bunch length <100 fs – 10 ps
Laser comb pulse shaping❖ Laser comb: multiple bunch trains are produced directly at the cathode !
❖ Pulses delayed by birefringent crystals (aBBO) and delay lines to fully control bunch inter-distance !
❖ Half-wave plates (HWP) for unbalancing intensity!❖ ramped charge
F. Villa et al., Proc. of the 2nd EAAC 2015
�� =
����1
vge
� 1
vgo
����Lcrystal
W
D1D2
D3
D4
Measured cross-correlation of the 5 laser pulses
Velocity Bunching P. O. Shea et al., Proc. of 2001 IEEE PAC, Chicago, USA (2001) p.704.!
M. Ferrario et al., Int. J. of Mod. Phys. B, 2006
Velocity Bunching❖ Velocity bunching for longitudinal compression: Sub-relativistic electrons ( < 1) injected into a traveling
wave cavity at zero crossing move more slowly than the RF wave ( ~ 1). The electron bunch slips back to an accelerating phase and becomes simultaneously accelerated and compressed!❖ Distance and duration optimized by tuning RF phase of first accelerating section!❖ Rectilinear trajectories => no coherent synchrotron radiation emission
�c�RF
Serafini, L., M. Ferrario. "Velocity bunching in photo-injectors" AIP conference proceedings. 2001. Ferrario, M.et al. "Experimental demonstration of emittance compensation with velocity bunching" PRL 104.5 2010
Driver and witness
Beam Energy (MeV) Energy spread (%)
Bunch duration (ps) Charge (pC) Hor Emittance!
(mm mrad)
Driver Beam 115.36(0.06) 0.39(0.02) 0.082(0.006) 200(10) 4.0(0.3)
Witness Beam 114.95(0.06) 0.138(0.006) <0.086(0.006) 20(2) 1.3(0.1)
Whole Beam 115.33(0.06) 0.39(0.02) 0.253(0.009) 22011) 4(0.3)
TimeSeparation ~ 0.77 (0.05) ps
�p
2
R. Pompili et al., Proc. of the 2nd EAAC 2015
Ramped bunch train
W
D1
D2
D3 D4
Beam Energy (MeV) Energy spread (%) Bunch duration (ps) Charge (pC)
Witness Beam 112.58(0.03) 0.084(0.003) <0.088(0.001) 24.04(0.28)
Driver 4 112.28(0.03) 0.159(0.003) 0.042(0.001) 74.91(0.46)
Driver 3 112.17(0.03) 0.112(0.003) 0.092(0.001) 69.39(0.36)
Driver 2 112.26(0.02) 0.087(0.003) 0.113(0.001) 36.34(0.20)
Driver 1 112.20(0.02) 0.045(0.004) <0.100(0.024) 36.34(0.20)
Whole Beam 112.27(0.03) 0.162(0.003) 1.275(0.003) 220.00(0.78)
Time Separation(ps) ! !W-D4 =1.58 (0.02) ~
!!
D4-D3 =1.38 (0.03) D3-D2 =0.80 (0.03) D2-D1 =0.91 (0.05)
3
2�p
⇡ �p
Measured Longitudinal Phase Space
Laser profile on photo-cathode
PWFA at SPARC_LAB
C-band structure
e-beam EOS diagnosticsPMQs triplets
Optical/THz !diagnostics
H2-filled!capillary
To the FEL
Quasi-non linear regime❖ Condition for blowout!
❖ Bubble formation w/o wave-breaking, λp is constant!❖ resonant scheme in blowout!
❖ Linear focusing force -> emittance is preserved !
❖ A measure of non-linearity is the normalized charge!
!
❖ Using low emittance, high brightness beam we have!
!❖ These conditions define quasi-non-linear regime!
❖ np= 1016cm-3, QD= 200 pC, σt=180 fs, σx=5.5 um → nb~5np and
nb
np> 1
Q̃ ⌘Nbk3pnp
= 4⇡kpreNb
Q̃ < 1nb
np> 1
Q̃ ⇡ 0.8
⌧ 1> 1
linear regime
blowout regime
J.B. Rosenzweig et al., "Plasma Wakefields in the Quasi-Nonlinear Regime" 500-504 (2010)!
P. Londrillo et al., "Numerical investigation of beam-driven PWFA in quasi-nonlinear regime” NIM 740, 236 (2014)
Plasma SourcePH2 = 10 mbar!
Total discharge duration :800 ns !
Voltage : 20 kV!
Peak current : 200 A!
Capacitor : 6 nF
Courtesy of M. P. Anania, A. Biagioni, D. Di Giovenale, F. Filippi, S. Pella
L = 3 cm
Hydrogengasgenerator
Measured current
ne = 1017 cm-3
H2-filled capillary discharge
Plasma SourcePH2 = 10 mbar!
Total discharge duration :800 ns !
Voltage : 20 kV!
Peak current : 200 A!
Capacitor : 6 nF
Courtesy of M. P. Anania, A. Biagioni, D. Di Giovenale, F. Filippi, S. Pella
L = 3 cm
Hydrogengasgenerator
Measured current
ne = 1017 cm-3
H2-filled capillary discharge
Plasma Characterization
Courtesy of M. P. Anania, A. Biagioni, F. Filippi, A. Ziegler
Plasma density measurement from Hα Stark broadening
ne = ne0e�↵t
↵ = 1.45 µs�1
Fit function:
The plasma density is controlled through the delay after the discharge
Start-to-End Simulation- σt=100 fs (rms) laser @ cathode
(blowout [1,2]) !- Laser pulse distance at cathode:
2.4 ps!- Driver-Witness distance at linac
exit: 560 fs
[1] Musumeci, P., et al., PRL 100, 244801 (2008) [2] Moody, J. T., et al. PRST AB 12, 070704 (2009)
Driver Witness
Charge (pC) 200 20
Energy (MeV) 117.5 116.75
Final focus (um) 5.5 3
Duration (fs) 180 35
en 4.5 2.4
Courtesy of R. Pompili
GPT simulation from the cathode to the plasma
Final focus with PMQs
Plasma Interaction
Courtesy of A. Marocchino, A. R. Rossi
Hybrid kinetic-fluid simulation by Architect*!! - PIC (bunch), fluid (plasma), 3-5 hours for 3 cm!! - Cross-checked with full PIC codes (ALaDyn)
np = 1016 cm-3 !
Ez ~ 1.1 GV/m
*F. Marocchino and F. Massimo, Proc. of the 2nd EAAC (2015)
ne/n0
−40
−20
0
20
40
0
5
10
15
nb/n0
0
2
4
6
8
Ez (GV/m)
−1.5
−1
−0.5
0
0.5
1
1.5
R (μ
m)
−3−2−10123
Er (GV/m)
−60
60
0
ξ (μm) -100-200-300
Er(GV/m)
flattens wake, reduces energy spread
Hollow driver beam manipulationWitness degradation occurs during bunch crossing • Driver acts as nonlinear lens !
• emittance growth !• Driver field is opposed to RF !
• lower compression
Hollow driver beam • No beam-beam effects !
• unperturbed witness !• Higher driver emittance (larger spot on cathode)
Courtesy of R. Pompili
0.3 mm mrad
22 fs
Conclusions
❖ Plasma-based acceleration is able to provide ultra-high, several GV/m, gradients !
❖ Plasma-based accelerators must provide high brightness beams!
❖ The resonant amplification of plasma waves by a train of HBEBs injected into the preformed plasma is one of the schemes proposed to this scope!
❖ Manipulation of electron beam phase spaces is mandatory to enhance the energy transfer and preserve the beam quality
Thank you!
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